Aluminum annealing furnace



May 11, 1965 A. WALKER ALUMINUM ANNEALING FURNACE 3 Sheets-Sheet 1 Filed Feb. 26, 1962 May 11, 1965 A. WALKER ALUMINUM ANNEALING FURNACE 3 Sheets-Sheet 2 Filed Feb. 25, 1962 IIO LIZILI'T T 920 mmvrm ARTHUR WALKER 6.0 A ORNEYS llo May 11, 1965 A. WALKER ALUMINUM ANNEALING FURNACE 3 Sheets-Sheet 3 Filed Feb. 26, 1962 INVENTOR.

ARTHUR WALKER [2 A ORNEYS United States Patent Filed Feb. 26, 1962, Ser. No. 175,777 Claims. Cl. 263-36) This invention relates to an industrial type of heat treating unit requiring a controlled gas atmosphere. More particularly, this invention relates to a radiant tube fired annealing furnace which is particularly adaptable for treating aluminum coils.

This invention is characterized by the provision of an annealing furnace through which aluminum coils are heated and cooled under a protected atmosphere in separate chambers. With such construction the greatest heating and cooling potential is present at the time when it is most necessary to perform the required work.

In the past, the annealing of aluminum coils has been done in a single chamber furnace wherein two methods were employed. In the first method, the work was extracted after heating and cooled in air. In the second method, the work was allowed to remain in the furnace for cooling in the atmosphere. The disadvantages of the first method are readily apparent to all persons skilled in the art, particularly for those alloys containing magnesium. The second method, while prohibiting oxidation, quite apparently tied up an expensive and valuable heating furnace for a period of eight to twelve hours during which period the furnace was not performing the primary function for which it was intended, namely that of heating. Another disadvantage is that when the heating chamber is also used as a cooling chamber it necessitates the problem that the interior of the furnace cools down during the cooling period and then has to be reheated when the next load is introduced into the furnace.

In the present invention where the heating is performed in one chamber and cooling in another chamber, many advantages have been achieved in that a smaller size heating unit may be utilized at a substantially reduced cost. Such a construction requires less fuel demand and consumption as well as less water demand and consumption. In addition, faster heating and cooling cycles are provided. While smaller loads in process are utilized, greater efiiciency is obtained during periods of partial production.

It is an object of the present invention to provide an improved annealing furnace for aluminum coils in which the furnace employs a highly efficient heating chamber and an equally efiicient cooling chamber which is connected on one end to the heating chamber.

Another object of the present invention is to provide a heat treating apparatus which is capable of being readily operated with a minimum amount of attention on the part of personnel and being of a design which enables installation in a substantially smaller space than previously had been used and at a substantial reduction in cost.

Still another object of the present invention is to provide an annealing furnace which utilizes a controlled inert protective gas atmosphere comprising a pair of longitudinally aligned chambers having their adjacent ends separated by a normally closed, transversely movable gas tight door, means for heating one of said chambers, means for cooling the other of said chambers, conveyor means extending lengthwise through said chambers for moving the work therethrough, means for directing the protective gas atmosphere into said chambers, means in said chambers for circulating the protective gas atmosphere throughout the chambers so as to envelope the work, and gas tight doors movable transversely across the other ends of said chambers.

A further object of the present invention is to provide See an annealing furnace of the aforementioned type wherein the means for heating said one chamber includes radiant tubes mounted vertically along the side walls of said one chamber and within'which a combustible mixture of gases are burned to radiate heat.

A still further object of the present invention is to provide an annealing furnace of the aforementioned type wherein the means for cooling the other of said chambers includes water cooling coils mounted along the side walls of said other chamber for removing heat from the work within said other chambers.

Another object of the present invention is to provide an annealing furnace of the aforementioned type wherein the conveyor means includes a plurality of longitudinally spaced, transversely extending power-driven rollers located at the bottom of said chambers.

Still another object of the present invention is to provide an annealing furnace of the aforementioned type wherein the means for circulating the protective gas at mosphere in said chambers includes a plurality of fans mounted in the top wall of said chambers.

Still another object of the present invention is to provide an annealing furnace of the aforementioned type wherein all of the doors are raised and lowered by the main furnace roll drive through a clutch system.

A further object of the present invention is to provide an annealing furnace of the aforementioned type wherein an additional cooling chamber is located at the other end of said cooling chamber and includes a plurality of cooling fans located in the side walls thereof and a trans- -versely movable door at the exit thereof.

A still further object of the present invention is to provide a method for purging an annealing furnace of the aforementioned type which has a plurality of holes in the door between the heating and cooling chambers whereby the cooling chamber is purged by introducing the protective atmosphere into the heating chamber which is fully pressurized to cause the atmosphere to flow through the holes in the door into the cooling chamber and prevents infiltration of air into the heating chamber, or whereby the heating chamber is purged by introducing the protective atmosphere into the cooling chamber where the atmosphere is preheated by the stock in the cooling chamber from where it passes into the heating chamber at an eleyated temperature through the holes provided in the last mentioned door.

-It is thus another object of the present invention to provide a simplified, low cost structure of the aforementioned type having certain advantages contributing to efficiency, reliability and long life as well as case of maintenance.

Other objects, advantages and novel details of construction of this invention will be made more apparent as this description proceeds, especially when considered in connection with the accompanying drawing, wherein:

FIGURE 1 is a top view of the present invention.

FIGURE 2 is a longitudinal cross section of the present invention.

FIGURE 3 is a sectional view taken on the line 3--3 of FIGURE 2.

FIGURE 4 is a sectional view taken on the line 44 of FIGURE 2.

FIGURE 5 is a sectional view taken on the line 5-5 of FIGURE 2.

. FIGURE 6 is a schematic representation of the main furnace roll drive, door drive and clutch system.

Briefly described, the invention consists of a furnace comprising a heating chamber and a cooling chamber. The heating chamber is heated by U-shaped radiant tubes mounted vertically therein. The cooling chamber is connected to the exit end of the heating chamber and is separated therefrom by a transversely movable door having a plurality of openings therein. High volume circulate-- ing fans are mounted in the heating and cooling chambers for circulating and controlling the flow of the protcctive gas atmosphere from a gas converter. An aux iliary cooling chamber may be provided at the exit end of the regular cooling chamber and is provided with circulating fans mounted in the side walls thereof for cooling the work therein.

The specific furnace installation as described herein is designed to process loads of 80,000 pounds of aluminum coil with approximately 12 hours in the heating chamber and 12 hours in the cooling chamber. Thus, the furnace will produce 80,000 pounds each 12 hours or a total of 160,000 pounds per day.

The annealing furnace of the present invention is designated by the numeral and includes a portion which is mounted below the level of the floor which is designated by the numeral 12. The annealing furnace 10 comprises a plurality of sections, namely the heating chamber 14 and the cooling chamber 16. An optional or auxiliary air cooling chamber 18 may be provided at the exit end of the cooling chamber 16.

The top and side walls 20 of the heating chamber 14 are formed from a high heat resistant refractory material such as insulating fire brick, mono-block insulation, or other suitable material. The exterior side of the walls 20 is provided with the usual structural steel frame 22 which consists of appropriate steel sheets, channels, angles, I-beams, or the like. A concrete slab 24 defines the bottom wall of the heating chamber 14 and is located in the floor pit 26 as is best illustrated in FIG. 3.

Heating chamber 14 has a series of vertically mounted, gas fired U tubes 30 adjacent each of the side Walls 20. Tubes 30 are of high temperature alloy and are equipped with radiant tube burners which are specifically designed for position type proportioning control to provide a constant supply of heat with no peaks of high fire or dead periods of low fire. This provides the uniformity of firing which is of utmost importance in heating aluminum coils. The ends of the tubes 30 extend above the top wall 20 of the chamber 14 as best indicated in FIG. 3.

On the inner sides of the radiant tubes 30 are provided a pair of longitudinally extending radiation baffies 32 which are adapted to radiate heat from the U-shaped tubes 30. The radiation bafiles 32 which are usually made from stainless steel are each provided with a plurality of openings 34 which permit circulation of the atmosphere therethrough. The openings 34 are arranged in two longitudinally extending rows as best shown in FIG. 2. The radiation baffles 32 are supported by the top wall 20 of the heating chamber 14 by means of a plurality of hangers 35 which are best illustrated in FIG. 3.

The U-shaped tube burners 30 per so which form no part of the present invention are identical in construction and a description of one will suffice for all. Gas and air are introduced separately into the tube 30 and are progressively mixed by a controlled diffusion after they have passed through the tube 30, thus providing an ideal luminous flame. The heating medium may be gas, oil or electricity. The tubes 30 are heated by the flame and in turn radiate their heat to the surrounding furnace wall and radiation bafile 32.

A plurality of high volume circulating fans 36 are divided in two rows and extend lengthwise of the heating chamber 14. as illustrated in FIG. 1. The fans 36 provide the high volume and velocity which is essential for circulating the protective gas atmosphere throughout the chamber 14. The atmosphere is directed into the chamber 14 from a gas converter, not shown. The fans 36 are of the squirrel cage impeller type which can develop greater pressure than the conventional propeller type fans. As a result, the fans 36 create a positive circulation by pulling in the gas atmosphere through the intakes 37 of the fans 36 and circulating the gas atmosphere in a downward direction over the heating tubes 30 and 4 upwards around the aluminum coils C as indicated by the arrows 39 in FIGURE 3.

Protective fan shrouds 38 made from suitable metal are supported in the heating chamber 14 and help in directing the protective gas atmosphere throughout its circular paths. Electrically driven motors 40 are carried by appropriate structural members 42 on top of the heating chamber 14. The motors 40 are appropriately connected to the shafts 44 of fans 36 for rotating the fans at a predetermined speed.

The cooling chamber 16 is provided with side walls 46 of suitable refractory material. The exterior side of the walls 46 and the top wall, which may be made from metal or appropriate refractory material, is provided with structural framing members 48 which may take the form of structural channels, angles, I-beams or the like. Adjacent the side walls 46 are a series of horizontal, finned water cooled coils 50. Banks of water cooled coils 50 are arranged adjacent each side wall 46 and are enclosed by a protective shroud 52 which extends lengthwise of the chamber 16. The shroud 52 forms a wall which aids in directing the protective gas atmosphere around the cooling coils 50. The cooling coils 50 remove the heat from the atmosphere which circulates throughout the heated work in the cooling chamber 16. Two pairs of high volume fans 54 are mounted in the top wall of the chamber 16. Metal shrouds 56 enclose the fans 54 leaving only the intakes 58 of the fans 54 open to the interior of the chamber 16. Electrically driven motors 60, which are carried by supports 61, are appropriately connected to the shafts 62 of the fans 54. The fans 54 are of the squirrel cage impeller type and create a positive circulation of the heated gas protective atmosphere downward over the cooling coils 50 and then upward around the aluminum coils C as indicated by the arrows 59 in FIG- URE 4.

At the exit end of the cooling chamber 16 may be provided an auxiliary or optional cooling chamber 18. The chamber 18 is provided with a suitable metal casing 66 which is supported by appropriate structural framing members 68. A plurality of fans 70 are mounted in the side walls of the chamber 18 for pulling air from the exterior of the chamber 18 and circulating the air around the heated work in the interior thereof. Generally the cooling chamber 16 cools the work to approximately 300 F. The auxiliary chamber 18 further reduces the temperature of the work or it may be used for cooling work brought from a different area.

At the entrance to the heating chamber 14 is provided a transversely movable door 72 which is supported by a cable 74 carried over a pulley 76 supported by the supporting member 78. Means to be subsequently described are provided for rotating the pulley 76 so as to raise or lower the door 72. A transversely movable door 80 is provided between the heating chamber 14 and the cooling chamber 16. The door 80 is carried by a cable 82 which is suspended on a pulley 84. The pulley 84 is carried by an appropriate structural member 86. A plurality of openings 86 are provided in the door 80 so as to provide a communication between the heating chamber 14 and the cooling chamber 16. A door 90 is provided at the exit end of the cooling chamber 16 and is suspended in the same manner as the door 72. In addition, the auxiliary cooling chamber 18 is provided with a door 92 at the exit end thereof which has a cable 94 attached thereto which surrounds a pulley 96. The pulley 96 is balanced by a suitable counterweight 98. The doors 72, 80, 90 and 92 are raised and lowered by the main furnace roll drive through a clutch system as will be subsequently explained.

At the entrance end of the heating chamber 14 is provided a loading section 100 which includes a plurality of power driven rollers 106 which are supported by suitable bearings 104 a predetermined distance above the ground. A plurality of longitudinally spaced, transversely extending rollers 106 which are mounted in all of the chambers 14, 16 and 18 are supported by appropriate bearings 108 carried by rows of longitudinally aligned rails 110. The rollers 106 in chambers 14-, 16 and 18 are in turn connected by appropriate shaft extensions 112 which extend through side walls of the chambers 14, 16 and 18 and are provided at the outer ends thereof with sprockets as will be subsequently described. The sprockets are in turn connected to a suitable chain drive mechanism, not shown, which rotates the extensions 112 and rollers 106 as required. The unloading section 116 is provided with power driven rollers 106 which are mounted similar to the rollers in the loading section 100.

The aluminum coils C are carried by an appropriate structural steel Work rack 120. The work rack 120 has various openings therein which permit the gas atmosphere to be circulated upwards therethrough into and around the aluminum coils C.

An appropriate walk way 130 is provided on the upper parts of the chambers 14 and 16 so as to permit a workman to reach the fans and the associated electrically driven motors for maintenance purposes.

As previously mentioned, the door 80 is provided with a plurality of openings 86. When the cooling chamber 16 is purged the gas atmosphere is introduced into the heating chamber 16 from a gas converter which causes the gas to flow through the holes 86 in the door 80 into the cooling chamber 16 and thereby prevent infiltration of air into the heating chamber 14. The gas converter, not shown, is connected to the cooling chamber 16 by means of a pipe 87.

When the heating chamber 14 is purged the gas atmosphere is introduced into the cooling chamber 16 and flows into the heating chamber 14 through the openings 86 provided in the door 80. This is the normal gas flow. The gas converter is connected to the heating chamber 16 by means of a pipe 89. In addition, the gas atmosphere is preheated by the stock in the cooling chamber 16 before it flows into the heating chamber 14. This method of purging is made possible by the provision of separate heating and cooling chambers.

The controlled atmosphere introduced into the furnace 10, to protect the aluminum coils from oxidizing during annealing, is prepared by an exothermic gas converter or generator. The gas generator is of the type well known in the art and utilizes an air-gas mixture which is burned in a reaction chamber after which the products of combustion are cooled and the excess water vapor removed. In such a reaction, natural gas may be used as the hydrocarbon.

In operation, when the heating chamber 14 is at the requisite temperature and gas pressure, the aluminum coils are introduced therein. The specific installation as described will process loads of 80,000 pounds with approximately twelve hours in the heating chamber. During this time the atmosphere is introduced into the chamber 16 so as to prevent air from entering therein. With the fans 36 circulating at the rated capacity, the gas atmosphere is circulated around the radiant tubes 30 following the circular paths indicated by the arrows 39 in FIG- URE 3. With this method, a closed system is maintained without air being pulled in or blown out the ends of the heating chamber. The heated atmosphere envelopes the aluminum coils C in process and thereby closely controls the surface appearance as well as the chemical and physical properties of the coils C.

After the work has been finished in the heating chamber 14, the power driven rollers are energized so as to move the aluminum coils into the cooling chamber 16 which is at the requisite temperature and pressure. The aluminum coils are maintained in the cooling chamber for approximately 12 hours where the controlled atmosphere which is cooled by the cooling coils 50 is effective to reduce the temperature of the aluminum coils to approximately 300" F. While the aluminum coils C are 6 being cooled in the cooling chamber 16, another load of aluminum coils may be introduced into the heating chamber 14. With such construction, the heating chamber 14 and the cooling chamber 16 may be utilized simultaneously to perform their required function.

After the temperature of the aluminum coils C has been reduced to approximately 300, generally after 12 hours, the coils may be moved into the auxiliary cooling chamber 18. The fans 70 pull the air in from outside of the furnace and circulate it around the aluminum coils C as indicated by the arrows 121 in FIG. 5. The auxiliary chambers 18 may also be utilized to cool additional Work brought from a different area.

As previously mentioned, one main furnace roll drive which is reversible is provided. The main furnace roll drive 130 is adapted to operate in timed sequence through a system of clutches the various doors and rollers of the entire annealing furnace.

FIGURE 6 illustrates schematically the main furnace roll drive 130 for the annealing furnace. The annealing furnace has a loading station 100, a heating chamber or furnace station 14, a cooling chamber or station 16, an optional air cooling chamber or station 18, and an unloading station 116. The furnace station 14 has the transversely movable charge door '72 at the entrance thereto. A second door is provided between the exit of the furnace station 14 and the entrance to the cooling station 16. A third door is provided between the exit of the cooling station 16 and the entrance to the air cooling station 18. Finally, a fourth door 92 is provided at the exit end of the air cooling station 18. The doors 72, 80, 90 and 92 are suspended in like manner for movement in vertical planes. As an example, the door 72 is suspended by appropriate wire ropes or cables 74 which are carried by pulleys 76 mounted on a shaft 151.

Means are provided for opening and closing the four doors and include air operated electrically actuated clutches which are controlled by air cylinders. Doors 72, 80, 90 and 92 are controlled by clutches 152, 153, 154 and 155 respectively. The clutche are each operated by an independent air cylinder 156. The clutches 152, 153, 154 and 155 are each interconnected with their respective door shaft 151 by suitable sprockets, pulleys and a drive chain 157.

As previously mentioned, each of the five stations is provided with transversely extending longitudinally spaced rollers 106. One end of each of the rollers 106 is provided with a pair of sprockets 166 and 168. Adjacent sprockets 166 and adjacent sprockets 168 are interconnected by chains 170 and 172 respectively.

The main furnace roll drive 130 is in turn connected to the rollers 106 of each of the five stat-ions through an air operated electrically actuated clutch which is operated by an air cylinder. Stations 100, 14, 16, 13 and 116 are controlled by clutches 173, 174, 175, 176 and 177 respectively. The clutches are each operated by an air cylinder 178. Each of the clutches 173, 174, 175, 176 and 177 is interconnected with the rollers 106 of its respective station by suitable sprockets and a drive chain 179. I

An electric motor 180 has a drive shaft which is connected to a speed reducer 132 through a coupling 184. The shaft of the speed reducer 182 has a sprocket 186 thereon which is connected by a chain 192 to a sprocket 188 carried on a shaft 190. The shaft 190 has the clutch 175 mounted thereon. The shaft 190 also has a pair of sprockets 194 and 196 thereon. A drive chain 198 connects sprocket 194 to sprocket 200 carried on shaft 202. Shaft 202 carries clutch 174. Sprocket196 is connected to sprocket 204 by a drive chain 206.

The sprocket 204 is mounted on a shaft 207 which has the clutch 176 thereon. The shaft 207 is connected by a chain 208 to a shaft 200 which has the clutch 177 thereon. The shaft 209 is connected by a chain 201 to a shaft 203 which carries the clutch 155. The shaft 190 is connected by a chain 210 to shaft 211 which is in turn tubes being carried by said top wall, said bafiies being effective to radiate the heat from said tubes into said work heating tunnel, said fans being efiective to forcibly circulate the gas in said heating zone through said fan chamber and said heating chambers to pick up heat from said radiant tubes and then through the exit open- I ings of said heating chambers to said tunnel in a pinand said bottom wall respectively to provide entrance openings and exit openings respectively for said cooling chambers, a transversely extending partition in said cooling zone near the upper edges of said inner walls and spaced from said top wall to define a second fan chamber therebetween, said last mentioned partition extending the entire length of the passageway in saidcooling zones, a plurality of fans in said second fan chamber supported by said top wall with entrance openings therefor in said last mentioned partition, the ends of said second fan chamher being connected to the entrance openings of said cooling chambers, said exit openings of said cooling chambers being connected to said tunnel in said cooling zone adjacent said bottom wall, a plurality of water cooled coils within each of said cooling chambers, said last mentioned fans being effective to forcibly circulate the gas insaid cooling zone through said second fan chamber and said cooling chambers across said coils to remove heat from the gas and then through the exit openings of said cooling chambers to said tunnel in a plurality of paths intersecting the path of movements of the work in said tunnel.

2. A heat-treating apparatus defined in claim 1 wherein said one zone is said heating zone.

FREDERICK L. MATTESON, JR, Examiner.

10 3. A heat-treating apparatus defined in claim 1 where in said intermediate door includes a plurality of relatively small ports for transfer of gas between heating and cooling zones when said intermediate door is closed.

4. A heat-treating apparatus defined in claim 1 wherein each of said radiation baffles includes a plurality of longitudinally spaced discharge ports which connect said heating chambers with the interior of said tunnel in the heating zone to permit passage of. the gas to said tunnel at points intermediate the entrance and exit openings of said heating chambers.

5. A heat-treating apparatus defined in claim 1 wherein an air cooling chamberis located at the exit end of said passageway, said air cooling chamber including a plurality of fans located in the side wall thereof for forcibly circulating air acrossthe work therein.

References Cited by the Examiner UNITED STATES PATENTS 1,060,414 4/13 Ayres 34-66 1,621,222 3/27 Robertson 263-28 1,949,716 3/34 Harsch 266-5 X 1,979,820 11/34 Bowling 148-161 2,039,429 5/36 Lydon.

2,083,638 6/37 Cope 266-5 2,232,391 2/41 Keller.

2,479,102 8/49 Dailey 263- 2,502,204 3/50 Cole 263-40 2,602,653 7/52 Cope 148-167 X 2,855,193 10/58 Gilbert 263-36 2,910,285 10/59 Harris 263-42 3,010,710 11/61 Bowman 263-36 X OTHER REFERENCES Darrah, W. A.: Annealing in Controlled Atmospheres, published by Continental Industrial Engineers, Inc., Chicago, Ill. (pages 6-10 relied on).

CHARLES SUKALO, Primary Examiner. 

1. A HEAT-TREATING APPARATUS OF THE INDIRECT TYPE FOR NON-FERROUS METALS COMPRISING AN ELONGATED HORIZONTAL PASSAGEWAY HAVING A TOP WALL, A BOTTOM WALL AND A PAIR OF SIDE WALLS, SAID PASSAGEWAY HAVING A HEATING ZONE AND A COOLING ZONE AND FORMING A GAS-TIGHT ENCLOSURE BETWEEN AN ENTRANCE END AND AN EXIT END THEREOF, TRANSVERSELY MOVABLE DOORS AT THE ENDS OF SAID PASSAGEWAY, A CONVEYOR FOR MOVING THE WORK SUCCESSIVELY THROUGH SAID HEATING AND COOLING ZONES, MEANS CONNECTED TO ONE OF SAID ZONES FOR DELIVERING AN INERT NON-OXIDIZING, NONCARBURIZING PROTECTIVE GAS THERETO, AN INTERMEDIATE DOOR IN SAID PASSAGEWAY BETWEEN SAID HEATING AND COOLING ZONES, A PAIR OF ELONGATED RADIATION BAFFLES AND COOLING METAL AT OPPOSITE SIDES OF SAID PASSAGEWAY SPACED FROM AND PARALLEL TO SAID SIDE WALLS TO DEFINE A PAIR OF HEATING CHAMBERS WITH SAID WALLS, SAID BAFFLES EXTENDING THE ENTIRE LENGTH OF THE PASSAGEWAY IN SAID HEATING ZONE AND FORMING THEREBETWEEN A WORK-HEATING TUNNEL, THE TOP AND BOTTOM EDGES OF SAID BAFFLES BEING SPACED FROM AND CLOSELY ADJACENT TO SAID TOP WALL AND SAID BOTTOM WALL RESPECTIVELY TO PROVIDE ENTRANCE OPENINGS AND EXIT OPENINGS RESPECTIVELY FOR SAID HEATING CHAMBERS, A TRANSVERSELY EXTENDING PARTITION NEAR THE UPPER EDGES OF SAID BAFFLES AND SPACED FROM SAID TOP WALL TO DEFINE A FAN CHAMBER THEREBETWEEN, SAID PARTITION EXTENDING THE ENTIRE LENGTH OF THE PASSAGEWAY IN SAID HEATING ZONE, A PLURALITY OF FANS IN SAID FAN CHAMBER SUPPORTED BY SAID TOP WALL WITH ENTRANCE OPENINGS THEREFOR IN SAID PARTITION, THE ENDS OF SAID FAN CHAMBER BEING CONNECTED TO THE ENTRANCE OPENINGS OF SAID HEATING CHAMBERS, SAID EXIT OPENINGS OF SAID HEATING CHAMBERS BEING CONNECTED TO SAID TUNNEL ADJACENT SAID BOTTOM WALL, A PLURALITY OF LONGITUDINALLY SPACED VERTICALLY EXTENDING ELONGATED RADIANT HEATER TUBES WITHIN EACH OF SAID HEATING CHAMBERS, THE UPPER ENDS OF SAID TUBES BEING CARRIED BY SAID TOP WALL, SAID BAFFLES BEING EFFECTIVE TO RADIATE THE HEAT FROM SAID TUBES INTO SAID WORK HEATING TUNNEL, SAID FANS BEING EFFECTIVE TO FORCIBLY CIRCULATE THE GAS IN SAID HEATING ZONE THROUGH SAID FAN CHAMBER AND SAID HEATING CHAMBERS TO PICK UP HEAT FROM SAID RADIANT TUBES AND THEN THROUGH THE EXIT OPENINGS OF SAID HEATING CHAMBERS TO SAID TUNNEL IN A PLURALITY OF PATHS INTERSECTING THE PATH OF MOVEMENT OF THE WORK IN SAID TUNNEL, A PAIR OF ELONGATED INNER WALLS IN SAID COOLING ZONE AT OPPOSITE SIDES OF SAID PASSAGEWAY SPACED FROM AND PARALLEL TO SAID SIDE WALLS TO DEFINE A PAIR OF COOLING CHAMBERS WITH SAID WALLS, SAID INNER WALLS EXTENDING THE ENTIRE LENGTH OF THE PASSAGEWAY IN SAID COOLING ZONES AND FORMING THEREBETWEEN A WORK-COOLING TUNNEL, THE TOP AND BOTTOM EDGES OF SAID INNER WALLS BEING SPACED FROM AND CLOSELY ADJACENT TO SAID TOP WALL AND SAID BOTTOM WALL RESPECTIVELY TO PROVIDE ENTRANCE OPENINGS AND EXIT OPENINGS RESPECTIVELY FOR SAID COOLING CHAMBERS, A TRANSVERSELY EXTENDING PARTITION IN SAID COOLING ZONE NEAR THE UPPER EDGES OF SAID INNER WALLS AND SPACED FROM SAID TOP WALL TO DEFINE A SECOND FAN CHAMBER THEREBETWEEN, SAID LAST MENTIONED PARTITION EXTENDING THE ENTIRE LENGTH OF THE PASSAGEWAY IN SAID COOLING ZONES, A PLURALITY OF FANS IN SAID SECOND FAN CHAMBER SUPPORTED BY SAID TOP WALL WITH ENTRANCE OPENINGS THEREFOR IN SAID LAST MENTIONED PARTITION, THE ENDS OF SAID SECOND FAN CHAMBER BEING CONNECTED TO THE ENTRANCE OPENINGS OF SAID COOLING CHAMBERS, SAID EXIT OPENINGS OF SAID COOLING CHAMBERS BEING CONNECTED TO SAID TUNNEL IN SAID COOLING ZONE ADJACENT SAID BOTTOM WALL, A PLURALITY OF WATER COOLED COILS WITHIN EACH OF SAID COOLING CHAMBERS, SAID LAST MENTIONED FANS BEING EFFECTIVE TO FORCIBLY CIRCULATE THE GAS IN SAID COOLING ZONE THROUGH SAID SECOND FAN CHAMBER AND SAID COOLING CHAMBERS ACROSS SAID COILS TO REMOVE HEAT FROM THE GAS AND THEN THROUGH THE EXIT OPENINGS OF SAID COOLING CHAMBERS TO SAID TUNNEL IN A PLURALITY OF PATHS INTERSECTING THE PATH OF MOVEMENTS OF THE WORK IN SAID TUNNEL. 